January 14, 2011
Alas, poor Pluto is no longer considered to be a planet by the scientists of the IAU (International Astronomical Union). Astronomers use three criteria for a body to be called a planet: 1) it has to be in orbit around the Sun. 2) it has to have enough mass to pull together so that it becomes nearly round. And 3) it has to have enough mass and gravitational pull to clear out other bodies in the space around it. Pluto meets the first two tests, but it does not have enough mass to clear the space around it (for example, if it had enough mass its gravity would pull a meteorite down so it crashes to the surface). So Pluto has been renamed a Dwarf Planet. All you kids who have memorized the planets in order from the sun will now have to stop at Neptune, the eighth planet from the sun.
Here’s some more information about Pluto from Space.com, a really neat site that you can use to find out all kinds of interesting facts about what’s out there.
Posted by: Seymour Simon
